Simon over at www.TechHead.co.uk put together this useful chart describing the max memory (RAM) limits for Windows 2008 (x86 and x64) and Windows 2008 R2 x64 and thought it was very useful so I'm posting here for reference.
http://www.techhead.co.uk/microsoft-windows-server-2008-and-2008-r2-maximum-memory-limits
| Version | Maximum Memory Limit (x64 Only) |
| Windows Server 2008 R2 Datacenter | 2TB |
| Windows Server 2008 R2 Enterprise | 2TB |
| Windows Server 2008 R2 for Itanium | 2TB |
| Windows Server 2008 R2 Foundation | 8GB |
| Windows Server 2008 R2 Standard | 32GB |
| Windows Web Server 2008 R2 | 32GB |
| Version | Max Memory Limit (x32) | Max Memory Limit (x64) |
| Windows Server 2008 Datacenter | 64GB | 2TB |
| Windows Server 2008 Enterprise | 64GB | 2TB |
| Windows Server 2008 Standard | 4GB | 32GB |
| Windows Small Business Server 2008 | 4GB | 32GB |
| Windows Web Server 2008 | 4GB | 32GB |
